Base station hand-off mechanism for cellular communication system

ABSTRACT

A channel hand-off control mechanism for a cellular communication network uses the same channels employed for communications between base stations of adjacent cells and a mobile transceiver, as the mobile transceiver moves between those cells, in order to locate the mobile transceiver relative to the base stations, so that the acquiring base station may readily place a narrowbeam channel on the mobile transceiver at hand-off. Each base station employs a phased array antenna, which allows the base station to controllably define its antenna coverage pattern with respect to any mobile transceiver, so as to minimize interference from one or more other transceivers, reducing frequency reuse distance.

FIELD OF THE INVENTION

[0001] The present invention relates in general to cellularcommunication systems, and is particularly directed to a new andimproved communication control mechanism for controlling the hand-off offrequency channels through which communications are conducted betweenbase stations of adjacent cells and a mobile transceiver as the mobiletransceiver moves between those cells.

BACKGROUND OF THE INVENTION

[0002] Wireless (cellular) communication service providers customarilysupply wireless communication capability to (mobile) subscribers locatedwithin a geographic area, through the use of a relatively limited numberof communication channels. In order to optimize coverage within thegeographical area of interest, the service provider typically subdividesthe area into a cluster or multiple clusters of base stations. Inaddition, in order to minimize interference from adjacent or nearbycells, the service provider may employ some form of frequencyreallocation (or reuse) scheme, such as that described in the U.S. Pat.No. 4,144,496, as a non-limiting example.

[0003] In such a spatially distributed or ‘cluster’ networkarchitecture, a fixed number of sectors (i) are served by a cluster of(k) base stations. This has the effect of subdividing the number ofavailable channels N by the product of i and k, namely by (i*k).Unfortunately, with today's expanding traffic, particularly in denselypopulated urban areas, service providers face the eventuality of runningout of channels to meet demand.

[0004] One solution is to construct more base stations and reduce powerlevels—which is both hardware intensive and expensive. Another scheme isto reuse channels in time (TDMA) or in frequency (CDMA). Otherapproaches, such as described in the above-referenced patent, includedynamic allocation of frequencies or channels to accommodate channeldemand. Initially, the relatively poor efficiency of frequencyallocation schemes was not a significant problem as the demand was smalland the number of available channels was more than adequate. However, asdemand increased, new channel assignment and frequency reuse strategieswere developed.

[0005] Such schemes have included sectorization of cells to minimizeinterference, and dynamic allocation or ‘borrowing’ of channels fromother cells with a cluster, to meet unbalanced demand within thecluster. A new and promising approach is to spatially separate channelsusing switched or steered antenna beams. The overall objective of anystrategy is to maximize the number of channels available, subject to anacceptable carrier (C) to interference (I) ratio, with the currentindustry standard being a figure of merit (or C/I ratio) of 18 dB.

[0006] Sectorization is a technique that uses fixed beams formed bydirectional antenna (phased) arrays installed at the base stations todivide the cell into an integral number of smaller cells. This techniqueserves to reduce interference to the base station, by attenuatingchannel interference to those mobile subscribers who are not located inthat sector's beam. It also reduces interference to the mobilesubscriber, by attenuating channel interference from base stationstransmitting in a direction that is predominately away from the locationof the mobile subscriber. However, as the number of sectors increases,the number of channels per sector necessarily decreases, therebyreducing the figure of merit. Ideally, at the time of systeminstallation, there would be no sectorization, which would greatlyincrease system capacity.

[0007] Regardless of the channel allocation mechanism employed, whenevera mobile subscriber moves from one cell to another, it is necessary tochange the frequency channel used to conduct communications with thebase station in the ‘old’ cell from which the mobile transceiver isdeparting to a new frequency channel used to conduct communications withthe base station in the ‘new’ cell which the mobile transceiver isentering.

[0008] Techniques using steered beam antennas have unique problemsaccomplishing this handoff between cells. In particular, the ‘new’ cellhas the problem of where to point its narrowbeam antenna. The mobilesubscriber is waiting on transmission from the new base station totransmit on the new frequency. If the new base station points the beamin the wrong direction, then the mobile subscriber sees no signal, doesnot synchronize and does not transmit. After the elapse of a prescribedperiod of time with no communication, the call will be dropped. Theproblem then is for the new base station to determine the correct beamto the mobile subscriber.

[0009] One mechanism for performing such frequency channelreuse/reallocation (or hand-off from the previous base station to thenew base station) is described in the U.S. patent to Forssen et al, U.S.Pat. No. 5,615,409. This scheme involves the base station using an‘intermediate’ channel to determine the direction of the mobiletransceiver relative to it. It then assigns the mobile transceiver to anavailable narrowbeam channel. Because this technique requires what couldotherwise be used for a regular communication channel be employed as anintermediate construct channel to determine the direction of the mobiletransceiver, it necessarily reduces the number of available preciousresources (channels).

SUMMARY OF THE INVENTION

[0010] In accordance with the present invention, this drawback iseffectively obviated by a channel hand-off communication controlmechanism that uses the very channels that are employed forcommunications between base stations of adjacent cells and a mobiletransceiver as the mobile transceiver moves between those cells, tolocate the mobile transceiver relative to the base stations, so that theacquiring base station may readily place a narrowbeam channel on themobile transceiver at hand-off. Each base station employs a phased arrayantenna, which allows the base station to controllably define itsantenna coverage pattern with respect to any mobile transceiver, so asto minimize interference from one or more other transceivers, andthereby reduce frequency reuse distance.

[0011] Pursuant to a first embodiment of the invention, when the qualityof a narrowbeam link between the mobile subscriber and an alreadyacquired cell base station indicates that the mobile transceiver isapproaching a cell boundary with a new cell, the already acquired basestation will initiate a hand-off sequence with the acquiring basestation in the new cell to which the mobile subscriber is moving. Forthis purpose, the current base station will forward a message to the newbase station that a channel hand-off is to commence. This hand-offinitiating message will contain the identification of the communicationchannel currently employed by the mobile transceiver.

[0012] In response to this message, the acquiring base station employsone of the antenna elements of its phased array antenna to transmit anomnidirectional burst on a new communication channel to which mobiletransceiver is to tune itself for conducting communications with theacquiring base station at hand-off, when the mobile transceiver enterscell. In response this burst signal on the new channel, the mobiletransceiver transmits a reply signal on the new channel, which isprocessed by the acquiring base station to derive a steering vectorrepresentative of the direction of the mobile transceiver relative tothe new base station.

[0013] The new base station employs this derived steering vector toadjust the directivity pattern of its phased array antenna, so as toplace a narrowbeam pattern of the new communication channel in thedirection of mobile transceiver, completing the hand-off. The new basestation proceeds to conduct narrow beam communications with the mobiletransceiver on the new communication channel. Using its ability tocontrol the directivity of the narrowbeam lobe by way of its phasedarray antenna, the new base station continues to communicate with andtrack the mobile transceiver as long as the mobile transceiver islocated in the new cell.

[0014] In a second embodiment of the invention, the acquiring basestation a ‘sectorized’ burst in place of an omni burst of the firstembodiment to locate the mobile subscriber. This sectorized burst isconfined to a prescribed spatial sector sourced from the new basestation toward the current cell in which the mobile subscriber iscurrently located.

[0015] In a third embodiment of the invention, the base station of thecurrent cell from which the mobile transceiver is about to depart intothe new cell determines the direction of the mobile transceiver relativeto the already acquired base station, and generates a first steeringvector associated with this direction. This steering vector is conveyedas part of the hand-off initiating message to the new or acquiring basestation. In response to this first steering vector message, the new basestation generates a second steering vector, representative of thedirection of the mobile transceiver relative to that base station forthe new communication frequency channel to be used between the mobiletransceiver and the new base station at channel hand-off. Using thissecond steering vector, the new base station adjusts the directivitypattern of its phased array antenna, so as to place a narrowbeam patternof the new communication channel in the direction of the mobiletransceiver.

[0016] When the mobile subscriber responds on the new channel, hand-offis complete between the base stations, and the mobile transceiverthereafter communicates with the second base station as it enters intoand travels through the new cell. The new base station then proceeds toconduct narrow beam communications with the mobile transceiver on thenew communication channel, using its phased array antenna to track andcommunicate with the mobile transceiver as long as the mobiletransceiver is located in the new cell.

[0017] In a fourth embodiment of the invention, the new or acquiringbase station ‘pretunes’ its transceiver to the ‘old’ or ‘pre hand-off’frequency employed by the current or already acquired base station, inorder to determine the direction of the mobile subscriber, prior tochannel hand-off. In response to a pre hand-off message, the new basestation uses its phased-array antenna to place a narrowbeam pattern forthe current channel being employed by the already acquired base stationin the general direction of the cell in which the mobile subscriber iscurrently located.

[0018] The new base station then monitors the current channel to derivea steering vector representative of the direction of the mobiletransceiver relative to the new base station. At hand-off, the new basestation employs the steering vector derived for the previous channel toplace a narrowbeam lobe for the new channel in the direction of themobile subscriber. When the mobile subscriber responds on the newnarrowbeam channel, hand-off is complete between the base stations, andthe mobile transceiver thereafter communicates with the new base stationas it enters into and travels through new cell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 diagrammatically illustrates adjacent cells of a cellularcommunication network, and associated base stations of which employphased array antennas for narrowbeam communications with a mobilesubscriber;

[0020]FIG. 2 is a cellular system diagram associated with a first ‘omni’burst embodiment of the present invention;

[0021]FIG. 3 sets forth a communication flow sequence associated withthe ‘omni’ burst embodiment of FIG. 2;

[0022]FIG. 4 is a cellular system diagram associated with a second‘sectorized’ burst embodiment of the present invention;

[0023]FIG. 5 is a communication flow sequence associated with the‘sectorized’ burst embodiment of FIG. 4;

[0024]FIG. 6 sets forth a communication flow sequence associated with athird embodiment of the invention, in which the base station of the cellfrom which the mobile transceiver is about to depart determines thedirection of the mobile transceiver and transmits a steering vectorassociated with this direction to the new base station; and

[0025]FIG. 7 sets forth a communication flow sequence associated with afourth embodiment of the present invention, in which the new basestation ‘pretunes’ its transceiver to the ‘old’ frequency to determinethe direction of the mobile subscriber, prior to hand-off.

DETAILED DESCRIPTION

[0026] Before describing the frequency hand-off control mechanism inaccordance with the present invention, it should be observed that theinvention resides primarily in what is effectively a prescribedarrangement of conventional communication circuits and associateddigital signal processing components and an attendant base stationcontrol program, that controls the operations of such circuits andcomponents. Consequently, the configuration of such circuits andcomponents and the manner in which they are interfaced with othercommunication system equipment have, for the most part, been illustratedin the drawings by readily understandable block diagrams, which showonly those specific details that are pertinent to the present invention,so as not to obscure the disclosure with details which will be readilyapparent to those skilled in the art having the benefit of thedescription herein. Thus, the block diagram illustrations and associatedflow charts of the supervisory base station control program areprimarily intended to show the major components of the system in aconvenient functional grouping and processing sequence, whereby thepresent invention may be more readily understood.

[0027] As described briefly above, and as diagrammatically illustratedin FIG. 1, pursuant to a first embodiment of the invention, each cellbase station 10 employs a phased array antenna 12 to which transceiverequipment 14 of the base station is coupled. The use of a phased arrayantenna allows the base station to controllably define its antennacoverage pattern with respect to any mobile transceiver 21, whichminimizes interference from one or more other transceivers, and therebyreduces frequency reuse distance.

[0028] Omni Burst (FIGS. 2 and 3)

[0029] A first embodiment of the frequency allocation control mechanismof the present invention will now be described with reference to themobile transceiver cellular system diagram of FIG. 2 and thecommunication flow sequence of FIG. 3. As shown in FIG. 2, a mobiletransceiver 21 traveling through a first cell 20 is approaching theboundary 23 between cell 20 and a second (immediately adjacent) cell 30.As mobile transceiver 21 travels through the cell 20, it communicateswith that cell's base station over an assigned frequency channel.

[0030] The narrowbeam directivity pattern 27 of this channel iscontinually updated in the direction of the mobile transceiver 21 bymeans of an adjustable steering vector that controls the operation ofthe base station's phased array antenna 29. As a non-limiting, butpreferred embodiment, each base station's phased array antenna may beconfigured as described in co-pending U.S. patent application Ser. No.09/081,476, filed May 19, 1998, by R. Hildebrand et al, entitled:“Circular Phased Array Antenna Having Non-Uniform Angular SeparationsBetween Successively Adjacent Elements,” assigned to the assignee of thepresent application and the disclosure of which is incorporated herein.

[0031] In addition, although the steering vector algorithm is notlimited to any particular implementation, non-limiting examples of thealgorithm include the PSF algorithm described in U.S. Pat. No. 4,255,791to P. Martin, entitled: “Signal Processing System,” issued Mar. 10,1981, and the “Maximum SNR Method,” described in the text “Introductionto Adaptive Arrays,” by R. Monzingo et al, published 1980, by Wiley andSons, N.Y.

[0032] Alternatively, and in accordance with a preferred embodiment ofthe invention, the steering vector algorithm may execute a directivitypattern control mechanism of the type described in co-pending U.S.patent application Ser. No. 09/081,287, filed May 19, 1998, by KarenHalford et al, entitled: “Bootstrapped, Piecewise-Optimum DirectivityControl Mechanism for Setting Weighting Coefficients of Phased ArrayAntenna, assigned to the assignee of the present application and thedisclosure of which is incorporated herein.

[0033] In the course of base station 25 within cell 20 monitoring thequality of the link, when the quality measurement on the mobiletransceiver 21 indicates that the transceiver is in the vicinity of thecell boundary 23, base station 25 initiates the communication sequenceshown in FIG. 3 with base station 35 in the ‘acquiring’ cell 30. At step301, using a dedicated inter base station communication control link,base station 25 forwards a message to the base station 35 that a channelhand-off is to commence.

[0034] This message will contain the identification of the communicationchannel currently employed by the transceiver 21. In response to thismessage, at step 303, base station 35 uses one of the antenna elementsof its phased array antenna 39 to transmit an omnidirectional burst onthe new communication channel to which mobile transceiver 21 is to tuneitself for conducting communications with the base station 35, when themobile transceiver enters cell 35. In a preferred embodiment, thisbroadbeam energy burst is set at a transmission power level of NP, whereN is ratio of the average gain of the phased array antenna to the gainof a single antenna element of the phased array antenna, and P is thepower at a single element required for the energy burst to close thecommunication link with the mobile transceiver 21 at cell boundary 23 atthe full gain of the phased array antenna.

[0035] At step 305, in response to receipt of this signal, mobiletransceiver 21 transmits a reply signal on the new channel. In step 307,base station 35 monitors the (omnidirectional) burst from the mobiletransceiver by means of the full reception capability of its phasedarray antenna 39 base station 35. In step 309, it processes the receivedsignal to determine the direction of the mobile transceiver 21 relativeto the second base station 35. For this purpose, a steering vectorsignal processing mechanism of the type described above may be employed.

[0036] Having determined the direction of the mobile transceiver 21relative to base station 35, in step 311, the base station 35 adjuststhe directivity pattern 37 of its phased array antenna 39, so as toplace a narrowbeam pattern of the new communication channel in thedirection of mobile transceiver 21. The average power allocated to eachelement of the phased array antenna is equal to the above-describedvalue of P.

[0037] Once it has completed hand-off of the mobile transceiver from thebase station 25, and acquired the mobile transceiver 21, in step 313,base station 35 proceeds to conduct narrow beam communications with themobile transceiver 21 on the new communication channel. Using itsability to control the directivity of the narrowbeam lobe by way of itsphased array antenna, base station 35 continues to communicate with andtrack the mobile transceiver 21 as long as the mobile transceiver islocated in the cell 30.

[0038] Sectorized Burst (FIGS. 4 and 5)

[0039] A modification of the first embodiment of the frequencyallocation control mechanism of the present invention, which employs asectorized beam, will be now described with reference to the mobiletransceiver cellular system diagram of FIG. 4 and the communication flowsequence of FIG. 5. As in the embodiment shown in FIG. 2, as a mobiletransceiver 21 traveling through a first cell 20 approaches the boundary23 between cell 20 and a second (immediately adjacent) cell 30, the linkquality measurement conducted by base station 25 or the mobiletransceiver 21 will indicate that the mobile transceiver 21 is in thevicinity of the cell boundary 23, and base station 25 will initiate thecommunication sequence shown in FIG. 5 with base station 35.

[0040] At step 501, using the system backhaul, base station 25 forwardsa message to base station 35 that a channel hand-off is to commence. Asin the first embodiment, this message will contain the identification ofthe communication channel currently employed by the transceiver 21. Inresponse to this message, at step 503, base station 35 employs itsphased array antenna 39 to transmit a ‘sectorized’ burst on the newcommunication channel to which mobile transceiver 21 is to tune itselffor conducting communications with the base station 35. As shown in FIG.4, this sectorized burst is confined to a prescribed spatial sector 41sourced from the base station 35 toward the cell 20. As a non-limitingexample, sector 41 may subtend an angle of 120°, which is effective toencompass the geographical region containing the mobile transceiver 21.

[0041] The power level of this sectorized transmission is set at atransmission power level of NP/M, where N is ratio of the average gainof the phased array antenna to the gain of one antenna element of thephased array antenna, P is the power required for the energy burst toestablish a communication link with the mobile transceiver 21 at thecell boundary 23 at the full gain of the phased array antenna, and M isthe ratio of the angle subtended by the spatial sector to 360°.

[0042] At step 505, as in the first embodiment, in response to receiptof this signal, mobile transceiver 21 transmits a reply signal on thenew channel. In step 507, base station 35 monitors the (omnidirectional)response from the mobile transceiver and then processes the receivedsignal in step 509 to derive a steering vector representative of thedirection of the mobile transceiver 21 relative to the second basestation 35.

[0043] Having determined the direction of the mobile transceiver 21relative to it, in step 511, the base station 35 adjusts the directivitypattern of its phased array antenna 39, so as to place a narrowbeampattern of the new communication channel in the direction of mobiletransceiver 21, just as in the first embodiment. In step 513, withchannel hand-off completed, the second base station conducts narrow beamcommunications with the mobile transceiver 21 on the new communicationchannel, and continues to communicate with and track the mobiletransceiver 21 as long as the mobile transceiver is located in the cell30.

[0044] Steering Vector Passed to New Base Station (FIG. 6)

[0045] A third embodiment of the handoff control mechanism of thepresent invention, shown in the channel hand-off flow sequence of FIG.6, begins at step 601, in which the base station 25 of the current cell20 from which the mobile transceiver is about to depart into adjacentcell 30 determines the direction of the mobile transceiver 21 relativeto the base station 25, and generates a first steering vector associatedwith this direction. In step 603, this steering vector is conveyed aspart of the hand-off initiating message conveyed from the current basestation 25 to new base station 35.

[0046] In response to this first steering vector message, at step 605,the new base station 35 generates a second steering vector,representative of the direction of the mobile transceiver relative tothe base station 35 for a new communication frequency channel to be usedbetween the mobile transceiver 21 and the new base station 35, atchannel hand-off. Using this second steering vector, in step 607, basestation 35 adjusts the directivity pattern of its phased array antenna,so as to place a narrowbeam pattern of the new communication channel inthe direction of mobile transceiver 21.

[0047] When the mobile subscriber 21 responds on the new channel,hand-off is complete between the base stations, and the mobiletransceiver 21 communicates with the second base station 35 as it entersinto and travels through cell 30. In step 609, having completed hand-offand acquired the mobile transceiver 21, the new base station 35 proceedsto conduct narrow beam communications with the mobile transceiver 21 onthe new communication channel. Using its phased array antenna, basestation 35 then continues to tune its narrowbeam channel, so as to trackand communicate with the mobile transceiver 21 as long as the mobiletransceiver is located in the cell 30.

[0048] New Base Station Pretunes to Mobile Subscriber (FIG. 7)

[0049] A modification of the third embodiment of the frequencyallocation control mechanism of the present invention, in which the newbase station 35 ‘pretunes’ its transceiver to the ‘old’ or ‘prehand-off’ frequency employed by the current base station 25, in order todetermine the direction of the mobile subscriber, prior to channelhand-off, is shown in the channel hand-off flow sequence of FIG. 7. Atstep 701 (in anticipation of hand-off), the base station 25 of thecurrent cell 20 from which the mobile transceiver is about to departinto adjacent cell 30 transmits an orderwire message to the new station35, that a hand-off is to take place.

[0050] In response to this pre hand-off message, at step 703, the newbase station 35 in cell 30 uses its phased-array antenna to place anarrow beam pattern (for the current channel being employed by the basestation 25 and the base station 35), in the direction of cell 20. Instep 705, the new base station 35 monitors the current (‘old’) channelto derive a steering vector representative of the direction of themobile transceiver 21 relative to the base station 35. When hand-offoccurs, in step 707, the new base station generates a steering vectorfor the new channel in accordance with that derived for the previouschannel. In step 709, acquiring base station 35 uses this new steeringvector to place a narrowbeam lobe for the new channel in the directionof the mobile subscriber 21.

[0051] When the mobile subscriber 21 responds on the new narrowbeamchannel, hand-off is complete between the base stations, and the mobiletransceiver 21 communicates with the second base station 35 as it entersinto and travels through cell 30. In step 711, having completed hand-offand acquired the mobile transceiver 21, the new base station 35 proceedsto conduct narrow beam communications with the mobile transceiver 21 onthe new communication channel. Using its phased array antenna, basestation 35 then continues to tune its narrowbeam channel, so as to trackand communicate with the mobile transceiver 21 as long as the mobiletransceiver is located in the cell 30.

[0052] As will be appreciated from the foregoing description, theundesirable usurping of what could otherwise be used for a regularcommunication channel, as an intermediate construct channel to determinethe direction of the mobile transceiver, is effectively obviated by thehand-off mechanism of the present invention, which employs the very samechannels for communications between base stations and the mobiletransceiver, as the mobile transceiver moves between adjacent cells, tolocate the mobile transceiver relative to the base stations, so that theacquiring base station may readily place a narrowbeam channel on themobile transceiver at hand-off. Each base station employs a phased arrayantenna, which allows the base station to controllably define itsantenna coverage pattern with respect to any mobile transceiver, so asto minimize interference from one or more other transceivers, andthereby reduce frequency reuse distance.

What is claimed:
 1. For use with a cellular wireless communicationsystem having a plurality of geographically distributed cells, each ofwhich contains a respective base station with which one or more mobiletransceivers communicate over assigned communication channels, a methodof controlling the transfer of a mobile transceiver, communicating overa first communication channel with a first base station of a first cell,to a second communication channel through which said mobile transceivercommunicates with a second base station of a second cell, in the courseof said mobile transceiver moving from said first cell to said secondcell, said method comprising the steps of: (a) providing antennas atsaid first and second base stations through which narrowbeam directivitypatterns for said first and second communication channels may bedirected toward said mobile transceiver; and (b) at said second basestation, directing a narrowbeam directivity pattern of said secondcommunication channel from said second base station toward said mobilesubscriber in accordance with a steering vector measurement made uponone of said first and second communication channels by one of said firstand second base stations.
 2. A method according to claim 1 , whereinstep (b) comprises the steps of: (b1) transmitting, from said secondbase station on said second communication channel, a broad beam energyburst that is effective to stimulate said mobile transceiver to transmiton said second communication channel; and (b2) in response to receipt atsaid second base station of a transmission from said mobile transceiveron said second communication channel, determining the direction of saidmobile transceiver relative to said second base station, and adjustingthe transmission of energy on said second communication channel fromsaid second base station to a reduced beam width in the direction ofsaid mobile transceiver relative to said second base station.
 3. Amethod according to claim 1 , further including the step of: (c)maintaining communication on said second communication channel betweensaid second base station and said mobile transceiver at a reduced beamwidth in the direction of said mobile transceiver relative to saidsecond base station, while said mobile transceiver is located in saidsecond cell.
 4. A method according to claim 2 , wherein step (b1)comprises transmitting said broad beam energy burst as anomnidirectional energy burst relative to said second base station.
 5. Amethod according to claim 2 , wherein step (b1) comprises transmittingsaid broad beam energy burst as a less than omnidirectional energy burstrelative to said second base station.
 6. A method according to claim 5 ,wherein step (b1) comprises confining transmission of said broad beamenergy burst to a prescribed spatial sector from said second basestation toward said first cell.
 7. A method according to claim 2 ,wherein said second base station contains a phased array antenna, by wayof which communication with said mobile transceiver is conducted, andwherein step (b1) comprises transmitting said broad beam energy burst asan omnidirectional energy burst from a single antenna element of saidphased array antenna.
 8. A method according to claim 7 , wherein step(b1) comprises transmitting said broad beam energy burst from saidsingle antenna element at a transmission power level of NP, where N isratio of the average gain of said phased array antenna to the gain ofone antenna element of said phased array antenna, and P is the powerrequired for said energy burst to establish a communication link withsaid mobile transceiver at a boundary of said second cell at the fullgain of said phased array antenna.
 9. A method according to claim 3 ,wherein step (c) comprises transmitting over said second communicationchannel to said mobile transceiver using the reduced beam width obtainedby said phased array antenna, in which the average power allocated toeach element of said phased array antenna is the power required for saidenergy burst to establish a communication link with said mobiletransceiver at a boundary of said second cell at the full gain of saidphased array antenna.
 10. A method according to claim 2 , wherein saidsecond base station contains a phased array antenna, by way of whichtransmission of said broad beam energy burst is confined to a prescribedspatial sector from said second base station toward said first cell. 11.A method according to claim 10 , wherein step (b1) comprisestransmitting said broad beam energy burst from said phased array antennaat a transmission power level of NP/M, where N is ratio of the averagegain of said phased array antenna to the gain of one antenna element ofsaid phased array antenna, P is the power required for said energy burstto establish a communication link with said mobile transceiver at aboundary of said second cell at the full gain of said phased arrayantenna, and M is the ratio of the angle subtended by said prescribedspatial sector to 360°.
 12. A method according to claim 11 , whereinstep (b2) comprises transmitting over said second communication channelto said mobile transceiver using said reduced beam width obtained bysaid phased array antenna, in which the average power allocated to eachelement of said phased array antenna is equal to P.
 13. A methodaccording to claim 1 , wherein step (b) comprises the steps of: (b1) atsaid first base station, determining the direction of said mobiletransceiver relative to said first base station, and conveying to saidsecond base station first steering vector information representative ofthe direction of said mobile transceiver relative to said first basestation; (b2) at said second base station, generating a second steeringvector, representative of the direction of said mobile transceiverrelative to said second base station, in accordance with said firststeering vector information conveyed thereto from said first basestation; and (b3) transmitting energy on said second communicationchannel at a confined beam width in said direction of said mobiletransceiver relative to said second base station.
 14. A method accordingto claim 13 , further including the step of: (b4) refining said secondsteering vector, as necessary, while said mobile transceiver is locatedin said second cell, to maintain communication over said secondcommunication channel between said second base station and said mobiletransceiver, at a reduced beam width in the direction of said mobiletransceiver relative to said second base station.
 15. A method accordingto claim 13 , wherein said second base station contains a phased arrayantenna, by way of which communication with said mobile transceiver isconducted, and wherein step (b3) comprises transmitting energy on saidsecond communication channel at a confined beam width obtained by saidphased array antenna, in said direction of said mobile transceiverrelative to said second base station.
 16. A method according to claim 1, wherein step (b) comprises the steps of: at said second base station,(b1) while said mobile transceiver is located in said first cell and istransmitting on said first communication channel, monitoringtransmissions therefrom by way of a phased array antenna, anddetermining therefrom a steering vector representative of the directionof said mobile transceiver relative to said second base station, (b2)tuning a transceiver for conducting communications with said mobiletransceiver on said second communication channel, and adjustingparameters of said phased array antenna to form a confined width beamfor said second communication channel in said direction of said mobiletransceiver relative to said second base station, and (b3) transmittingenergy, by way of said phased array antenna, on said secondcommunication channel at said confined width beam in said direction ofsaid mobile transceiver relative to said second base station, and whichis effective to stimulate said mobile transceiver to transmit on saidsecond communication channel; and at said mobile transceiver, (b4) inresponse to receipt of energy transmitted thereto on said secondcommunication channel from said second base station in step (b3),conducting communications with said second base station on said secondcommunication channel.
 17. A method according to claim 16 , furtherincluding the step of: at said second base station, (b5) refining saidsteering vector, as necessary, while said mobile transceiver is locatedin said second cell, to maintain communication over said secondcommunication channel between said second base station and said mobiletransceiver, at a reduced width beam in the direction of said mobiletransceiver relative to said second base station.
 18. For use with acellular wireless communication system having a plurality ofgeographically distributed cells, each of which contains a respectivebase station with which one or more mobile transceivers communicate overassigned communication channels, a method of controlling the transfer ofa mobile transceiver, communicating over a first communication channelwith a first base station of a first cell, to a second communicationchannel through which said mobile transceiver communicates with a secondbase station of a second cell, in the course of said mobile transceivermoving from said first cell to said second cell, said method comprisingthe steps of: (a) transmitting, from said second base station on saidsecond communication channel, a broad beam energy burst that iseffective to stimulate said mobile transceiver to transmit on saidsecond communication channel; (b) in response to receipt at said secondbase station of a transmission from said mobile transceiver on saidsecond communication channel, determining the direction of said mobiletransceiver relative to said second base station, and adjusting thetransmission of energy on said second communication channel from saidsecond base station to a reduced beam width in the direction of saidmobile transceiver relative to said second base station; and (c)thereafter maintaining communication on said second communicationchannel between said second base station and said mobile transceiver ata reduced beam width in the direction of said mobile transceiverrelative to said second base station, while said mobile transceiver islocated in said second cell.
 19. A method according to claim 18 ,wherein step (a) comprises transmitting said broad beam energy burst asan omnidirectional energy burst relative to said second base station.20. A method according to claim 18 , wherein step (a) comprisestransmitting said broad beam energy burst as a less than omnidirectionalenergy burst relative to said second base station.
 21. A methodaccording to claim 20 , wherein step (a) comprises confiningtransmission of said broad beam energy burst to a prescribed spatialsector from said second base station toward said first cell.
 22. Amethod according to claim 18 , wherein said second base station containsa phased array antenna, by way of which communication with said mobiletransceiver is conducted, and wherein step (a) comprises transmittingsaid broad beam energy burst as an omnidirectional energy burst from asingle antenna element of said phased array antenna.
 23. A methodaccording to claim 22 , wherein step (a) comprises transmitting saidbroad beam energy burst from said single antenna element at atransmission power level of NP, where N is ratio of the average gain ofsaid phased array antenna to the gain of one antenna element of saidphased array antenna, and P is the power required for said energy burstto establish a communication link with said mobile transceiver at aboundary of said second cell at the full gain of said phased arrayantenna.
 24. A method according to claim 23 , wherein step (b) comprisestransmitting over said second communication channel to said mobiletransceiver using the reduced beam width obtained by said phased arrayantenna, in which the average power allocated to each element of saidphased array antenna is equal to P.
 25. A method according to claim 18 ,wherein said second base station contains a phased array antenna, by wayof which transmission of said broad beam energy burst is confined instep (a) to a prescribed spatial sector from said second base stationtoward said first cell.
 26. A method according to claim 25 , whereinstep (a) comprises transmitting said broad beam energy burst from saidphased array antenna at a transmission power level of NP/M, where N isratio of the average gain of said phased array antenna to the gain ofone antenna element of said phased array antenna, P is the powerrequired for said energy burst to establish a communication link withsaid mobile transceiver at a boundary of said second cell at the fullgain of said phased array antenna, and M is the ratio of the anglesubtended by said prescribed spatial sector to 360°.
 27. A methodaccording to claim 26 , wherein step (b) comprises transmitting oversaid second communication channel to said mobile transceiver using saidreduced beam width obtained by said phased array antenna, in which theaverage power allocated to each element of said phased array antenna isequal to P.
 28. For use with a cellular wireless communication systemhaving a plurality of geographically distributed cells, each of whichcontains a respective base station with which one or more mobiletransceivers communicate over assigned communication channels, a methodof controlling the transfer of a mobile transceiver, communicating overa first communication channel with a first base station of a first cell,to a second communication channel through which said mobile transceivercommunicates with a second base station of a second cell, in the courseof said mobile transceiver moving from said first cell to said secondcell, said method comprising the steps of: (a) at said first basestation, determining the direction of said mobile transceiver relativeto said first base station, and conveying to said second base stationfirst steering vector information representative of the direction ofsaid mobile transceiver relative to said first base station; and (b) atsaid second base station, generating a second steering vector,representative of the direction of said mobile transceiver relative tosaid second base station, in accordance with said first steering vectorinformation conveyed thereto from said first base station; and (c)transmitting energy on said second communication channel at a confinedbeam width in said direction of said mobile transceiver relative to saidsecond base station.
 29. A method according to claim 28 , furtherincluding the step of: (d) refining said second steering vector, asnecessary, while said mobile transceiver is located in said second cell,to maintain communication over said second communication channel betweensaid second base station and said mobile transceiver, at a reduced beamwidth in the direction of said mobile transceiver relative to saidsecond base station.
 30. A method according to claim 28 , wherein saidsecond base station contains a phased array antenna, by way of whichcommunication with said mobile transceiver is conducted, and whereinstep (c) comprises transmitting energy on said second communicationchannel at a confined beam width obtained by said phased array antenna,in said direction of said mobile transceiver relative to said secondbase station.
 31. For use with a cellular wireless communication systemhaving a plurality of geographically distributed cells, each of whichcontains a respective base station with which one or more mobiletransceivers communicate over assigned communication channels, a methodof controlling the transfer of a mobile transceiver, communicating overa first communication channel with a first base station of a first cell,to a second communication channel through which said mobile transceivercommunicates with a second base station of a second cell, in the courseof said mobile transceiver moving from said first cell to said secondcell, said method comprising the steps of: at said second base station,(a) while said mobile transceiver is located in said first cell and istransmitting on said first communication channel, monitoringtransmissions therefrom by way of a phased array antenna, anddetermining therefrom a steering vector representative of the directionof said mobile transceiver relative to said second base station, (b)tuning a transceiver for conducting communications with said mobiletransceiver on said second communication channel, and adjustingparameters of said phased array antenna to form a confined width beamfor said second communication channel in said direction of said mobiletransceiver relative to said second base station, and (c) transmittingenergy, by way of said phased array antenna, on said secondcommunication channel at said confined width beam in said direction ofsaid mobile transceiver relative to said second base station, and whichis effective to stimulate said mobile transceiver to transmit on saidsecond communication channel; and at said mobile transceiver, (d) inresponse to receipt of energy transmitted thereto on said secondcommunication channel from said second base station in step (c),conducting communications with said second base station on said secondcommunication channel.
 32. A method according to claim 31 , furtherincluding the step of: at said second base station, (e) refining saidsteering vector, as necessary, while said mobile transceiver is locatedin said second cell, to maintain communication over said secondcommunication channel between said second base station and said mobiletransceiver, at a reduced width beam in the direction of said mobiletransceiver relative to said second base station.